The preparation of the introductory paper to this Conference has presented two particular problems. First, as always, there was the risk that it would contain too many references to aspects which would be dealt with in greater detail — and possibly contradicted subsequently. Secondly, the title of the Conference, ‘By-Products and Wastes in Animal Feeding’, seemed to be at variance with a definition of waste, ‘a resource arising (in agriculture) where the cost and complexity of using that resource is greater than the returns from using it’, which I had used at a similar Conference a year ago (Raymond, 1977) and which might imply that ‘waste’, once utilized, is no longer ‘waste’. But this is really semantics; the aim of this Conference is to bring together the latest information on whether resources which have conventionally been considered ‘wastes’ can effectively and economically be utilized in new animal feeding systems. The concept of economic use is vital. I strongly believe that we must reject the idea that there is some sort of moral imperative to use wastes; if this is not economic then their use must involve the misuse of some other resource within the total production system.

The situation is of course dynamic; effective research and development (R and D) can transform yesterday's waste resource into a new productive asset. Further, the economic environment is not static; for example, changes in relative costs of feedstuffs mean that farmers will this winter feed large quantities of straw which in 1972 they would have burnt in the field, while high cereal prices mean that more non-tariff components, including by-products, are now being included in least-cost livestock rations. Thus it is worth examining some of the factors that have led to the current interest in the role of by-products and waste materials in animal feeding setting aside any marginal objection to this use of ‘waste’.